MECHENG 382 Lecture Notes - Linear Elasticity, Correspondence Principle, Crazing
Document Summary
Effect of temperature on elastic modulus of polymers. Thermoplastics: only secondary bonds between chains, modulus dictated by energy, large strains cause fracture, modulus 1 gpa. Thermoplastics: no bonding between chains, modulus dictated by entropy, large strains permanent deformation as chains slide over each other. Elastomers: a few covalent cross-links & secondary bonds between chains chains, modulus dictated primarily by energy, large strains involve bond rupture and yielding (permanent deformation) Elastomers: a few covalent cross-links, modulus dictated by entropy, large strains. Effects of time on deformation of polymers: chain motion impeded by tangles activation energy needs to be overcome, molecules and atoms vibrate with a frequency . Probability (/second) that obstacles to motion will be overcome = exp q/rt. For a given stress: strain as hold time or as t : both reversible and permanent deformation (creep) may have time- & temperature- dependence, this sort of model gives rise to hysteresis.